LEVELS OF ORGANIZATION
It's vital to consider how the components are arranged and how they could logically fit together and operate efficiently before you start studying the structure and function of the human body and its numerous parts. The many levels of organisation that impact body form and function are depicted in Figure 1-2.
Life on a Chemical Level-Basis
The organisation of the body begins at the chemical level, as seen in Figure 1-2. There are approximately 100 distinct chemical building units in nature, known as atoms, which are tiny spheres of substance that are invisible to the naked eye. The human body, like everything else in our universe, is made up of atoms. Molecules are bigger chemical groupings formed by the combination of atoms. Molecules, in turn, frequently interact with additional atoms and molecules to produce macromole cules, which are larger and more complex compounds.
The unique and complicated connections that exist between atoms, molecules, and macromolecules in living material constitute cytoplasm (SYE-toe-plazm), a semifluid matrix-type substance that is fundamental to human existence. Death occurs if appropriate chemical element interactions are not maintained. Maintaining the sort of chemical order necessary for life in the cytoplasm necessitates the expenditure of energy. Important information on the chemistry of life will be explored in greater depth in Chapter 2.
Organelle Level
Chemical components can be arranged into a variety of structures called organelles (or-gan-ELZ), the next level of organisation, within bigger units called cells (see Figure 1-2). Organelles are groupings of molecules that are arranged in a way that allows them to perform a certain function. Each cell's ability to life is determined by the total of these structures. Organelles cannot live outside of the cell, yet a cell cannot survive without them.
Over a half-dozen organelles have been discovered. The "power house" of cells, mitochondria (my-toe-KON-dree ah), provides the energy needed for the cell to carry out day-to-day functions, growth, and repair (see Figure 1-2); The Golgi (GOL-jee) apparatus is a kind of digestive apparatus. Endoplasmic reticulum, the transport channels within the cell that function as "highways" for the flow of chemicals, offers a "packing" service to the cell by storing material for future internal use or export from the cell. Organelles and their functions are covered in detail in Chapter 3.
Cellular Level
Life's features are the consequence of a structure and function hierarchy that starts with the arrangement of atoms, molecules, and macromolecules. The next organisational phase is further organisation, which results in organelles. The most essential role of the chemical and organelle levels of organisation, however, is to provide the fundamental building blocks and specialised structures necessary for the next higher level of body structure—the cellular level.
The smallest and most abundant structural units that possess and show the essential characteristics of living stuff are cells. What is the total number of cells in the human body? According to one estimate, a 150-pound adult human body contains 100,000,000,000,000. If you can't figure out what this number means (it has 14 zeros following it), it's 100 trillions! or 100,000 billions! or 100 million millions!
Each cell is characterised by a single nucleus surrounded by cytoplasm, which includes the various organelles necessary for specialised function. Although all cells have some characteristics, they specialise or differentiate to accomplish specific activities. Fat cells, for example, have structural changes that allow them to store lipid material. Figure 1-2 shows the specialised cells that line the tubes of the respiratory system. They release mucus and are coated by cilia, which are hairlike projections (SIL-ee-ah). These cells aid in the protection of the respiratory system against dust and other pollutants breathed. Other physically and functionally specialised cells include muscle, bone, neuron, and blood cells.
Tissue level
The tissue level, as shown in Figure 1-2, is the next higher level of structure after the cell. Tissues are the next level in the progression or hierarchy of living matter structure. A tissue, by definition, is a collection of numerous similar cells that have been specialised to fulfil a certain job. The matrix, or nonliving intercellular material, surrounds tissue cells in various quantities and types.
Epithelial, connective, muscular, and nerve tissue are the four primary or principal tissue types. In light of the human body's complexity, this is a relatively limited list of main tissues. However, each of the four main tissues may be further split into a variety of specialised subtypes. The bodily tissues work together to satisfy all of the body's structural and functional demands.
Figure 1-2 shows a specific kind of epithelium that lines the tubes of the respiratory system as an example. Epithelial tissues come in a variety of shapes and sizes. Some are designed to create sheets that coat the body's surface, while others line bodily cavities or protect the respiratory and digestive systems' passages. Chapter 4 will go into the specifics of tissue structure and function.
Organ Level
Organs are more complicated than tissues in terms of structure. An organ is a collection of several tissues that are organised in such a way that they may perform a certain function when combined. Each lung, for example, is an example of organ organisation: muscle and specialised connective tissues create the many tubes that transport air, epithelial cells line the tiny air sacs, and nerve tissues govern air flow and muscular activity.
Tissues are rarely seen alone. Instead, they create organs that reflect distinct but functionally complex operational units when they are linked together. Each organ has its own shape, size, appearance, and location in the body, and the pattern of tissues that make it up may be used to identify it. Organs include the lungs, heart, brain, kidneys, liver, and spleen, to name a few.
System Level
The most complicated of the body's component organisational units is the system. The system level of organisation involves a variety of organs that are structured in such a way that they may perform complicated functions for the body, functions that are tailored to satisfy specific demands. Integumentary, skeletal, muscular, nervous, endocrine, circulatory, lymphatic/immune, respiratory, digestive, urinary, and reproductive systems make up the human body. The systems that work together to meet the body's basic demands will be discussed next.
Protection from the outside
The skin, also known as the integumentary system, is essential for living. Its main purpose is to keep you safe. It protects underlying tissue from dangerous bacteria, prevents most chemicals from entering, and reduces mechanical damage to underlying tissues. The skin also serves as a complex sensory organ, regulating body temperature, synthesising vital chemicals and hormones, and synthesising important chemicals and hormones. The skin and its appendages, including as hair, nails, and specialised glands, make up the integumentary system (Figure 1-3). Dermatology is the study of the skin and its disorders.
Movement and support
To support and move the body, the skeletal and muscular systems collaborate (Figure 1-4).
The skeletal system is made up of bones and associated tissues like cartilage and ligaments that work together to give a strong foundation for support and protection to the body. Furthermore, the skeletal system allows movement through joints, or articulations. Bones also store minerals and have a role in hematopoiesis, or the production of blood cells.
The organs of the muscular system are individual muscles. The muscular system also includes smooth, or involuntary, muscles and the cardiac muscle of the heart, in addition to voluntary, or skeletal, muscles that have the ability to contract when stimulated and are under conscious control. Muscles are responsible for not only producing movement (or maintaining body posture), but also for generating heat necessary for maintaining a consistent core temperature.
Figure 1 - 4 Systems that provide support and movement.
Control, integration, and communication
The body's many structures must be coordinated and regulated in order for it to operate as a whole. This important duty is carried out by the neurological and endocrine systems (Figure 1-5).
The nervous system includes the brain, spinal cord, and nerves. Communication, integration, and regulation of bodily processes are among the major tasks of this complex system. The production, transmission, integration, and identification of specific nerve impulses are used to carry out these activities.
The nerve impulse is responsible for the fast and accurate regulation of a variety of bodily functions. The nervous system's components recognise specific stimuli that impact the body, such as light, pressure, and temperature. Nervous impulses may then be produced to send this information to the brain, where it may be evaluated and appropriate action taken. Muscles contract and glands secrete as a result of nerve signals. The field of science that deals with the nervous system and its diseases is known as neurology or neurobiology.
The endocrine system is made up of glands that release hormone-like substances straight into the bloodstream. The organs of the endocrine system, also known as ductless glands, fulfil the same broad activities as the nervous system, namely communication, integration, and regulation.
Fast-traveling nerve impulses in the nervous system offer rapid, short control. Hormone production by the endocrine system offers slower but longer-lasting regulation. The organs that are acted on and respond in some manner by a certain hormone are referred to as target organs.
Hormones control metabolism, growth and development, reproduction, and a variety of other bodily functions. They serve critical roles in fluid and electrolyte balance, acid-base balance, and energy metabolism, among other things.
Endocrine glands include the pituitary, pineal, hypothalamus, thyroid, parathyroids, adrenals, pancreas, ovaries, testes, thymus, and placenta. Endocrinology is the study of the endocrine glands and their hormones.
Figure 1 - 5 Systems that provide communication, control and integration
Defense and transportation
For all of the body's cells to benefit from specific organ functions—for example, food intake and waste output—a network must exist to allow chemicals to be sent back and forth between the organ, or system, level and the cellular level. As a result, hormones generated by the endocrine system, for example, might reach skeletal system cells as needed. The cardiovascular system is the body's distribution network.
The cardiovascular and lymphatic systems of the body are used by the immunological response, which is the body's defensive mechanism (Figure 1-6).
The heart and a closed system of vessels termed arteries, veins, and capillaries make up the cardiovascular system.
The circulatory system's blood is pumped by the heart around a circular circle or circuit of vessels as it travels through the body, as the name indicates.
The cardiovascular system's principal role is transportation. It is self-evident that the body requires an effective transportation system.
The continuous passage of oxygen and carbon dioxide, nutrients, hormones, waste materials, and other essential chemicals is a critical transportation need.
Lymph, lymphatic arteries, lymph nodes, and specialist lymphatic organs including the thymus and spleen make up the lymphatic system.
The lymphatic system's tasks include the transport of fluids and some big molecules, such as proteins, from the tissue spaces surrounding cells to the blood, as well as the transport of fat-related nutrients from the digestive tract to the general circulation. Lymphatic tissue is directly linked with the immune response. The immune system, on the other hand, is described as a functioning system rather than a collection of specialised organs. It is made up of specialised cells and chemicals that provide disease resistance and protection.
The effective functioning of our lymphatic system and immunity is essential for our capacity to resist infections, fight cancer, and many other diseases. Immunology is the study of how the immune system works.
Figure 1 - 6 Systems that provide transportation and defense.
Processing, regulation, and upkeep are all things that need to be taken care of.
The respiratory, digestive, and urinary systems all play a role in keeping the body's cells in a stable environment. Nutrients are formed when foods are broken down. In return for waste items that are removed, nutrients and oxygen are supplied to cells. Mechanisms that continually monitor and respond to the body's internal circumstances govern these activities (Figure 1-7).
The nose, throat, larynx, trachea, bronchi, and lungs are all organs of the respiratory system. These organs work together to allow air to flow into the alveoli, the lungs' small, thin-walled sacs. The alveoli are where oxygen from the air is exchanged for carbon dioxide, a waste product that is transported to the lungs by the blood to be expelled from the body.
The mouth, pharynx (throat), oesophagus, stomach, small intestine, large intestine, rectum, and anal canal are the major organs of the digestive system. The gastrointestinal, or Gl, tract is made up of several organs and is open on both ends. The digestive system's accessory organs aid in the correct functioning of the system but are not part of the GI tract itself. Teeth, tongue, salivary glands, liver, gallbladder, and pancreas are all accessory digestive organs.
Food that enters the gastrointestinal tract is digested, nutrients are absorbed, and the undigested residue is excreted as faeces. Gastroenterology is the scientific study of the gastrointestinal tract and its disorders. The two kidneys, the ureters, the bladder, and the urethra are all part of the urinary system. The kidneys' job is to "clear" or "clean" the blood of the many waste products that are constantly generated in the body cells by food metabolism.
Urine is the waste substance generated by the kidneys. It flows out of the kidneys and into the urinary bladder, where it is stored, through the two ureters. The urethra transports urine from the bladder to the exterior of the body.
The two kidneys, the ureters, the bladder, and the urethra are all part of the urinary system. The kidneys' job is to "clear" or "clean" the blood of the many waste products that are constantly generated in the body cells by food metabolism.
Figure 1 - 7 Systems involved with processing, regulation and maintenance.
Development and reproduction
Male and female reproductive systems work together to enable conception and development of children (Figure 1-8). The significance of normal reproductive system function differs significantly from the end result of "normal function" as assessed in any other human organ system. The survival of the genetic code, not the individual, is ensured by the correct functioning of the reproductive system. Furthermore, proper reproductive system activity results in the creation of hormones that allow for the development of sexual traits.
The gonads (testes) in the male reproductive system produce sperm; a number of genital ducts, including the vas deferens and urethra; accessory glands, such as the prostate gland, which contribute secretions important to reproductive function; and supporting structures, such as the penis and scrotum (genitalia). These structures work together to generate, transmit, and eventually deliver sperm into the female reproductive canal, where fertilisation can take place.
The ovaries are the female gonads. The uterus, uterine (Fallopian) tubes, and vagina are accessory organs. External accessory sex organs include the breasts, often known as mammary glands. The female reproductive organs are designed to generate sex cells or eggs, receive male sex cells, fertilise and transport sex cells to the uterus, and allow for the development, delivery, and nutrition of the progeny. Gynecology is the study of the female reproductive system.
Figure 1 - 8 Systems involved with reproduction and development.
Organism Level
The human body is unquestionably more than the sum of its parts. It's a brilliantly connected collection of dynamic buildings that can live and thrive in a harsh environment. The human body can not only replicate itself and repair and replace numerous damaged or ageing components on a continuous and predictable basis, but it can also maintain an astonishing number of variables that are necessary for humans to live healthy, productive lives. We can keep our bodies at a "normal" temperature.
We maintain consistent blood levels of numerous vital chemicals and nutrients; we have excellent disease prevention, waste removal, and coordinated movement; and we accurately and rapidly process sound, visual pictures, and other external inputs with remarkable regularity. These are only a few instances of how the many levels of structure in the human system allow for the display of life-like qualities.
It's all too tempting to conceive of each component or function in isolation from the body as a whole while studying the structure and function of the human body. Always keep in mind that you're dealing with knowledge about the complete human organism, not just information on the structure and function of a single organelle, cell, tissue, organ, or organ system. Don't restrict your learning to factual memorization. Instead, integrate and synthesise factual knowledge such that your understanding of human anatomy and function is not limited to a single body component but encompasses the entire body.
QUICK INSPECTION
1. Make a list of the seven organisational levels.
2. Name three different organelles.
3. Identify the four primary kinds of tissue.
4. Make a list of the eleven primary organ systems.
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